# Problems with vibrational frequency calculation

Hi everyone,

I have 2 questions regarding vibrational frequency calculation:

First, I tried to calculate anharmonic frequency for cation state of CHDBrI and CH2BrI however, these 2 outputs have error more or less like this:

TOSH[ 1] 152.42 VPT2[ 1] 152.42
TOSH[ 2] ******** VPT2[ 2] ********
TOSH[ 3] ******** VPT2[ 3] ********
TOSH[ 4] ******** VPT2[ 4] ********
TOSH[ 5] ******** VPT2[ 5] ********
TOSH[ 6] ******** VPT2[ 6] ********
TOSH[ 7] ******** VPT2[ 7] ********
TOSH[ 8] ******** VPT2[ 8] ********
TOSH[ 9] ******** VPT2[ 9] ********

and this is caused by an anomaly force fields as:

``````  ANHARMONIC CUBIC & QUARTIC FORCE FIELD (CM**-1)
``````

Eta[2,2,2]=-141.6199278108,
Eta[2,2,2,2]=40.1386941067,
Eta[2,2,3]=28865.6397657348,
Eta[2,2,2,3]=-28834.0623604823,
Eta[2,2,3,3]=111353.8012230565,
Eta[2,2,4]=41090.0032118632,
Eta[2,2,2,4]=-40846.4332420119,
Eta[2,2,4,4]=229680.9375796154,
Eta[2,2,5]=39725.2884111891,
Eta[2,2,2,5]=-39568.8296897450,
Eta[2,2,5,5]=210453.9831150707,
Eta[2,2,6]=47226.1907331729,

Does anybody know why this is happening? I do this using wB97M-V/Def2-QZVPPD level of theory for this calculation.

Secondly, is it possible to print more digit to the atomic vibration vector for more decimals, because by default it only print 3 decimals such as:

Mode: 1 2 3
Frequency: 152.27 538.53 651.03
Force Cnst: 0.7094 1.0631 1.5626
Red. Mass: 51.9291 6.2214 6.2573
IR Active: YES YES YES
IR Intens: 3.410 25.531 7.240
Raman Active: YES YES YES
X Y Z X Y Z X Y Z
C 0.148 -0.411 0.000 0.616 0.188 -0.000 -0.170 0.611 0.000
H 0.043 -0.371 -0.021 0.513 0.158 0.026 -0.094 0.531 0.058
I -0.395 0.024 -0.000 -0.040 -0.041 0.000 -0.020 -0.020 -0.000
Br 0.611 0.033 -0.000 -0.043 0.034 0.000 0.061 -0.075 -0.000
H 0.043 -0.371 0.021 0.513 0.158 -0.026 -0.094 0.531 -0.058
TransDip -0.059 -0.005 -0.000 0.159 0.029 0.000 -0.027 0.082 -0.000

Kind regards,

Eduardus

This is the input that i’ve used:

## User input:

\$molecule
\$end

\$rem
BASIS = def2-QZVPPD
ECP = def2-ECP
SCF_CONVERGENCE = 8
GUI = 2
JOB_TYPE = Frequency
METHOD = wB97M-V
SCF_MAX_CYCLES = 999
mem_total = 64000
XC_GRID = 3
ANHAR = TRUE
ISOTOPES = TRUE
SYMMETRY = TRUE
VIBMAN_PRINT = 4
\$end

\$isotopes
1 0
1
5 2.01410
\$end

The first problem looks like overflowing a formatted print, and I don’t think that the print format is user-controllable in either case. If you are a developer this could be easily fixed or else you can submit a feature request to Q-Chem.

Hi jherbert,

Thank you for your reply. I think this will be useful for my second problem.

However, in the first problem, I think the algorithm of QChem makes the force field very large, which makes a very big anharmonic frequency. This happened in both cation system that I mentioned. Do you have any idea how to deal with this problem?

No idea, as I have not used this particular feature in Q-Chem. It’s probably a good idea to try some variations to see if you can isolate the source of the problem. For example, I would not immediately jump in with a quadruple-zeta basis set, but instead would start with something much smaller. If possible, try it also without ECPs, and maybe with a different functional. Insofar as you get reasonable results, you can then add those things back in one at a time and see which one of those choices leads to the issue.